Optimized link training and management mechanism

ABSTRACT

In one embodiment, a converged protocol stack can be used to unify communications from a first communication protocol to a second communication protocol to provide for data transfer across a physical interconnect. This stack can be incorporated in an apparatus that includes a protocol stack for a first communication protocol including transaction and link layers, and a physical (PHY) unit coupled to the protocol stack to provide communication between the apparatus and a device coupled to the apparatus via a physical link. This PHY unit may include a physical unit circuit according to the second communication protocol. Other embodiments are described and claimed.

TECHNICAL FIELD

Embodiments relate to interconnect technologies.

BACKGROUND

To provide communication between different devices within a system, sometype of interconnect mechanism is used. A wide variety of suchinterconnects are possible depending on a system implementation.Oftentimes to enable two devices to communicate with each other, theyshare a common communication protocol.

One typical communication protocol for communications between devices ina computer system is a Peripheral Component Interconnect Express (PCIExpress™ (PCIe™)) communication protocol in accordance with links basedon the PCI Express™ Specification Base Specification version 3.0(published Nov. 18, 2010) (hereafter the PCIe™ Specification). Thiscommunication protocol is one example of a load/store input/output (IO)interconnect system. The communication between the devices is typicallyperformed serially according to this protocol at very high speeds.Various parameters regarding this protocol were developed with theintent to achieve maximum performance without regard to powerefficiency, as the PCIe™ communication protocol was developed in thecontext of desktop computers. As a result, many of its features do notscale down to lower power solutions that could be incorporated intomobile systems.

In addition to these power concerns with conventional load/storecommunication protocols, existing link management schemes are typicallyvery complex and involve a large number of states, causing a lengthyprocess to perform transitions between the states. This is due in partto existing link management mechanisms, which were developed tocomprehend multiple different form factor requirements such asconnectors, different system incorporations and so forth. One suchexample is link management in accordance with the PCIe™ communicationprotocol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high level block diagram of a protocol stack for acommunication protocol in accordance with an embodiment of the presentinvention.

FIG. 2 is a block diagram of a system-on-a-chip (SoC) in accordance withan embodiment of the present invention.

FIG. 3 is a block diagram of a physical unit in accordance with anotherembodiment of the present invention.

FIG. 4 is a block diagram showing further details of a protocol stack inaccordance with an embodiment of the present invention.

FIG. 5 is a state diagram for a link training state machine, which canbe part of a link manager in accordance with an embodiment of thepresent invention.

FIG. 6 is a flow diagram for the various states of a sideband mechanismin accordance with an embodiment of the present invention.

FIG. 7 is a flow diagram of a method in accordance with an embodiment ofthe present invention.

FIG. 8 is a block diagram of components present in a computer system inaccordance with an embodiment of the present invention.

FIG. 9 is a block diagram of an example system with which embodimentscan be used.

DETAILED DESCRIPTION

Embodiments may provide an input/output (IO) interconnect technologythat has low power, a load/store architecture, and is particularlysuited to use in mobile devices including cellular telephones such assmartphones, tablet computers, electronic readers, Ultrabooks™ and soforth.

In various embodiments, a protocol stack for a given communicationprotocol can be used with a physical unit of a different communicationprotocol, or at least a physical (PHY) unit different than the physicalunit for the given communication protocol. A physical unit includes botha logical layer and a physical or electrical layer that provides for theactual, physical communication of information signals over aninterconnect such as a link that links two independent semiconductordie, which can be two semiconductor die within a single integratedcircuit (IC) package or separate packages, coupled, e.g., via a circuitboard routing, trace or so forth. In addition the physical unit canperform framing/deframing of data packets, perform link training andinitialization, and process the data packets for delivery onto/receiptfrom a physical interconnect.

Although different implementations are possible, in one embodiment theprotocol stack may be of a conventional personal computer (PC)-basedcommunication protocol such as a Peripheral Component InterconnectExpress (PCI) Express™ (PCIe™)) communication protocol in accordancewith the PCI Express™ Specification Base Specification version 3.0(published Nov. 18, 2010) (hereafter the PCIe™ specification), a furtherversion that applies protocol extensions, or another such protocol,while the physical unit is not according to the PCIe™ communicationprotocol. This physical unit can be specially designed for purposes ofenabling low power operation to allow incorporation of a substantiallyunchanged PCIe™ upper protocol stack with this low power physicalcircuitry. In this way the broad legacy base of the PCIe™ communicationprotocol can be leveraged for ease of incorporation into portable andother non-PC-based form factors that operate at low power. Although thescope of the present invention is not limited in this regard, in oneembodiment this physical unit may be a physical unit adapted from amobile platform such as a so-called M-PHY according to the M-PHYSpecification Version 1.00.00—8 Feb. 2011 (MIPI Board Approved 28 Apr.2011) of the Mobile Industry Processor Interface (MIPI) Alliance(hereafter MIPI specification), which is a group that sets standards formobile computing devices. However, other low power physical units suchas according to other low power specifications such as used to coupletogether individual dies within a multi-chip package, or a custom lowpower solution can be used. As used herein, the term “low power” meansat a power consumption level below a conventional PC system, and whichmay be applicable to a wide variety of mobile and portable devices. Asan example, “low power” may be a physical unit that consumes less powerthan a conventional PCIe™ physical unit.

In this way, by converging a traditional PCIe™ protocol stack with adifferent type of physical unit, high amounts of reuse of legacycomponents that have been developed for PCIe™ can be leveraged forincorporation into a mobile or other portable or low power platform.

Embodiments also may leverage the recognition that existing load/storeIO technologies, particularly PCIe™, are designed with the intent toachieve maximum performance where power efficiency is not a primaryconcern, and thus do not scale down to low power applications. Bycombining portions of a conventional load/store protocol stack with aphysical unit of a low power design, embodiments may preserve theperformance advantages of PCIe™, while achieving best in class power atthe device and platform levels.

As such, embodiments may be software compatible with ubiquitous PCIe™architectures that have a large legacy base. In addition, embodimentsmay also enable direct PHY re-use of a mobile-designed PHY, e.g., aM-PHY. In this way, low active and idle power can be realized withefficient power/bit transferred, along with an approach that iselectromagnetic interface/radio frequency interface (EMI/RFI) friendly,as the PHY may operate at clock rates that do not interfere withassociated radios (since harmonics of the clock frequency for the PHY donot interfere with common radio frequencies at which typical radiosolutions operate (e.g., 1.8, 1.9, 2.4 gigahertz (GHz) or other suchradio frequencies).

Embodiments may further provide for architectural enhancements thatenable an optimized link training and management mechanism (LTSSM);optimized flow control and retry buffering and management mechanisms; anarchitected protocol for changing link operating mode; fasthardware-supported device state save and restore; and a consolidatedsideband mechanism for link management with optional in-band support.

In various embodiments, PCIe™ transaction and data link layers can beimplemented as part of a protocol stack with limited modifications toaccount for different link speeds and asymmetric links. In addition,revised link training and management may be provided to include supportfor multi-lane communications, asymmetric link configurations, sidebandconsolidation, and dynamic bandwidth scalability. Embodiments mayfurther provide support for bridging between existing PCIe™-based andnon-PCIe™-based logic and circuitry such as M-PHY logic and circuitry.

This layering approach enables existing software stacks (e.g., operatingsystem (OS), virtual machine managers and drivers) to run seamlessly ona different physical layer. The impact to the data link and transactionlayer is minimized and may include updating of timers related to updateacknowledgment frequency, replay timers and such.

Thus embodiments can limit some of the flexibility afforded in PCIe™systems, as this flexibility can in some cases create certaincomplexities in both PCIe™ systems and other systems. This is so, asboth of these protocols provide for a great deal of flexibility toenable plug-and-play capability. Instead, embodiments can tailor asolution that minimizes the amount of flexibility in a design, sincewhen incorporated into a given system, e.g., as a system on a chip (SoC)interconnected to another integrated circuit (IC), a known and fixedconfiguration occurs. Because it is known on implementation the exactconfiguration that is present, as both the SoC and the connected deviceare affixed within the platform, e.g., soldered to a circuit board ofthe system, no plug-and-play capability with regard to these devices isneeded and thus the greater flexibility inherent in a PCIe™ or otherPC-based communication protocol that enables seamless incorporation ofdifferent devices into a system with plug-and-play capability may not beneeded.

As one example, the SoC can act as a root complex that is implemented ina first IC, and is coupled to a second IC that may be a radio solution,which can include one or more devices of multiple wireless communicationdevices. Such devices can range from low power short range communicationsystems such as in accordance with a Bluetooth™ specification, localwireless communications such as a so-called WiFi™ system in accordancewith a given Institute of Electrical and Electronics Engineers (IEEE)802.11 standard, to a higher power wireless system such as a givencellular communication protocol such as a 3G or 4G communicationprotocol.

Referring now to FIG. 1, shown is a high level block diagram of aprotocol stack for a communication protocol in accordance with anembodiment of the present invention. As shown in FIG. 1, stack 100 canbe a combination of software, firmware and hardware within asemiconductor component such as an IC to provide for handling of datacommunication between the semiconductor device and another devicecoupled to it. In the embodiment of FIG. 1, a high level view is shownbeginning with a higher level software 110, which can be various typesof software that execute on a given platform. This higher level softwarecan include operating system (OS) software, firmware, applicationsoftware and so forth. Data to be communicated via an interconnect 140that may be a given physical interconnect that couples the semiconductordevice with another component can pass through various layers of aprotocol stack, generally shown within FIG. 1. As seen, portions of thisprotocol stack can be part of a conventional PCIe™ stack 120 and mayinclude a transaction layer 125 and a data link layer 128. In general,transaction layer 125 acts to generate transaction layer packets (TLP),which can be request or response-based packets separated by time,allowing the link to carry other traffic while the target device gathersdata for the response. The transaction layer further handlescredit-based flow control. Thus transaction layer 125 provides aninterface between a device's processing circuitry and the interconnectarchitecture, such as a data link layer and a physical layer. In thisregard, a primary responsibility of the transaction layer is theassembly and disassembly of packets (i.e., transaction layer packets(TLPs)), as well as handling credit-based flow control.

In turn, data link layer 128 may sequence TLPs that are generated by thetransaction layer and ensure reliable delivery of TLPs between twoendpoints (including handling error checking) and acknowledgementprocessing. Thus link layer 128 acts as an intermediate stage betweenthe transaction layer and the physical layer, and provides a reliablemechanism for exchanging TLPs between two components by a link. One sideof the link layer accepts TLPs assembled by the transaction layer,applies identifiers, calculates and applies an error detection code,e.g., cyclic recovery codes (CRC), and submits the modified TLPs to thephysical layer for transmission across a physical link to an externaldevice.

After processing in data link layer 128, packets can be communicated toa PHY unit 130. In general, PHY unit 130 may include a low power PHY134, which may include both logical layers and physical (includingelectrical) sub-layers. In one embodiment, the physical layerrepresented by PHY unit 130 physically transmits a packet to an externaldevice. The physical layer includes a transmit section to prepareoutgoing information for transmission and a receiver section to identifyand prepare received information before passing it to the link layer.The transmitter is supplied with symbols that are serialized andtransmitted to an external device. The receiver is supplied withserialized symbols from the external device and transforms the receivedsignals into a bitstream. The bitstream is de-serialized and supplied toa logical sub-block.

In one embodiment, low power PHY 134, which can be a given low power PHYeither developed specially or adapted from another PHY such as an M-PHY,can provide for processing of the packetized data for communicationalong interconnect 140. As further seen in FIG. 1, a link training andmanagement layer 132 (also referred to herein as link manager) may alsobe present within PHY unit 130. In various embodiments, link manager 132can include certain logic that can be implemented from anothercommunication protocol such as a PCIe™ protocol and specialized logic tohandle interfacing between the conventional, e.g., PCIe™ protocol stackabove, and the physical PHY 134 of a different protocol.

In the embodiment of FIG. 1, interconnect 140 can be implemented asdifferential pairs of wires that may be two pairs of unidirectionalwires. In some implementations, multiple sets of differential pairs maybe used to increase bandwidth. Note that according to the PCIe™communication protocol, the number of differential pairs in eachdirection is required to be the same. According to various embodiments,however, different numbers of pairs can be provided in each direction,which allows more efficient and lower power operation. This overallconverged stack and link 140 may be referred to as a Mobile ExpressPCIe™ interconnect or link. While shown at this high level in theembodiment of FIG. 1, understand the scope of the present invention isnot limited in this regard. That is, understand that the view shown inFIG. 1 is simply with regard to the protocol stack from the transactionlayer through the physical layer, along with higher level software, andvarious other circuitry of a SoC or other semiconductor device includingthis stack is not shown.

Referring now to FIG. 2, shown is a block diagram of a SoC in accordancewith an embodiment of the present invention. As shown in FIG. 2, SoC 200can be any type of SoC for implementation into various types ofplatforms, ranging from relatively small low power portable devices suchas smartphones, personal digital assistants (PDAs), tablet computers,netbooks, Ultrabooks™ and so forth, to more advanced SoCs that can beimplemented in higher level systems.

As seen in FIG. 2, SoC 200 may include one or more cores 210 ₀-210 _(n).Thus in various embodiments, a multicore SoC is possible, where thecores all may be homogeneous cores of a given architecture, e.g., anin-order or out-of-order processor. Or there can be heterogeneous cores,e.g., some relatively small low power cores, e.g., of an in-orderarchitecture, with additional cores present that may be of a larger andmore complicated architecture, e.g., an out-of-order architecture. Aprotocol stack enables communication of data between one or more ofthese cores and other components of a system. As seen, this stack caninclude software 215, which may be higher level software such as OS,firmware, and application level software that executes on one or more ofthe cores. In addition, the protocol stack includes a transaction layer220 and a data link layer 230. In various embodiments, these transactionand data link layers may be of a given communication protocol such as aPCIe™ protocol. Of course, layers of different protocol stacks such asin accordance with a universal serial bus (USB) protocol stack may bepresent in other embodiments. Also, in some implementations low powerPHY circuitry as described herein can be multiplexed with existingalternate protocol stacks.

Still referring to FIG. 2, in turn this protocol stack can couple to aphysical unit 240 that may include multiple physical units that canprovide for communication via multiple interconnects. In one embodiment,a first physical unit 250 may be a low power PHY unit that in oneembodiment may correspond to an M-PHY in accordance with the MIPIspecification to provide communication via a primary interconnect 280.In addition, a sideband (SB) PHY unit 244 may be present. In theembodiment shown, this sideband PHY unit may provide for communicationvia a sideband interconnect 270, which may be a consolidated sideband toprovide certain sideband information, e.g., at slower data rates thanprimary interconnect 280 that is coupled to first PHY 250. In someembodiments, the various layers of the protocol stack can have aseparate sideband coupling to this SB PHY 244 to enable communicationalong this sideband interconnect.

In addition, PHY unit 240 may further include an SB link manager 242that can be used to control SB PHY 244. In addition, a link training andstate manager 245 may be present and can be used to adapt the protocolstack, which is of a first communication protocol, to first PHY 250,which is of a second communication protocol, as well as providingoverall control of first PHY 250 and interconnect 280.

As further seen, various components may be present in first PHY 250.More specifically, transmitter and receiver circuitry (namely TX 253 andRX 254) may be present. In general, this circuitry may be used toperform serialization operations, deserialization operations along withthe transmission and receipt of data via primary interconnect 280. Asave state manager 251 may be present and can be used to save aconfiguration and other state information regarding first PHY 250 whenit is in a low-power state. Also, a coder 252 can be present to performline coding, e.g., according to an 8b/10b protocol.

As further seen in FIG. 2, a mechanical interface 258 may be present.This mechanical interface 258 may be a given interconnection to providecommunication from root complex 200, and more specifically to/from firstPHY 250 via primary interconnect 280. In various embodiments, thismechanical connection can be by way of pins of the semiconductor devicesuch as a ball grid array (BGA) or other surface mount, or platedthrough hole connection.

In addition to these main communication mechanisms, an additionalcommunication interface may be by way of a low power serial (LPS) PHYunit 255, coupled via a separate stack including a software layer 216, atransaction layer 221, and a link layer 231 between cores 210 and one ormore off-chip devices 260 a-c, which can be various low data rateperipheral devices such as sensors, accelerometers, temperature sensors,global positioning system (GPS) circuitry, compass circuitry,touch-screen circuitry, keyboard circuitry, mouse circuitry and soforth.

Note that in various embodiments, both the sideband interconnect 270 andprimary interconnect 280 can couple between SoC 200 and anothersemiconductor component, e.g., another IC, such as a multi-band radiosolution.

Again while the illustration of FIG. 2 is at a relatively high level,variations are possible. For example, it is possible to provide multiplelow power PHYs to enable higher rates of data communication, e.g., viamultiple channels, where each channel is associated with an independentPHY. Referring now to FIG. 3, shown is a block diagram of a physicalunit in accordance with another embodiment of the present invention. Asshown in FIG. 3, physical unit 300 includes a link training and statemanager 310. This state manager may be as described above, and can be acollection of logic to enable interfacing of a protocol stack of a firstcommunication protocol with a physical unit of a second, e.g., differentcommunication protocol.

As further seen in FIG. 3, link training and state manager 310 may be incommunication with multiple M-PHYs 320 ₀-320 _(n). By providing morethan one such PHY, higher rates of data communication can occur. Notethat while each M-PHY illustrated in FIG. 3 may include some amount oflogic to enable its individual, independent communications to occur, theoverall control of communications of these different M-PHYs may be vialink training and state manager 310. Also, understand that while aplurality of M-PHYs are shown in FIG. 3, in other embodiments, multiplePHY units of another type can be present, and further multipleheterogeneous PHY units can be provided. Note that each M-PHY unit canbe used either as part of a unique logical link, or in groups where agroup is associated with a single logical link. Each device maytypically consume a single logical link, although in some embodiments asingle physical device may consume multiple logical links, e.g., toprovide dedicated link resources for different functions of amulti-function component.

Referring now to FIG. 4, shown is a block diagram showing furtherdetails of a protocol stack in accordance with an embodiment of thepresent invention. As shown in FIG. 4, stack 400 includes various layersincluding a transaction layer 410, a data link layer 420, and a physicallayer 430. As described above, these different layers can be configuredusing either conventional transaction and data link portions of a PCIe™protocol stack, or modified versions of such stack to accommodateinteraction between these layers of this first communication protocoland a physical layer of another communication protocol, which in theembodiment of FIG. 4 may be M-PHYs according to the MIPI specification.

As seen in FIG. 4 with regard to a transmit direction in whichinformation is transmitted from protocol stack 400, incoming informationto the protocol stack, e.g., from other circuitry of a SoC such as acore or other processing logic, is received in a transmit packetassembler 412 of the transaction layer, which typically combines controland data paths to form a TLP. After being assembled into transmitpackets, which in various embodiment can be data packets having, e.g., 1to 4096 bytes (or of a smaller maximum allowed size, e.g., 128 or 256),the assembled packets are provided to a flow controller 414 whichdetermines whether sufficient flow control credits are available basedon the number required for the next TLP(s) queued for transmission andcontrols the injection of packets into data link layer 420. Morespecifically as seen, these injected packets are provided an errordetector and sequencer 422 which in one embodiment may generate a TLPsequence number and LCRC. As further seen, data link layer 420 furtherincludes a transmit messaging mechanism 426 that in turn generates DLLPsfor link management functions and is coupled to a data link transmitcontroller 425 which is a controller functionality for flow control anddata link integrity (ACK/NAK) mechanisms; note that this may besubdivided such that these functions are implemented using distinctlogic blocks.

As further seen, the processed data packets are provided to a retrybuffer 424, which holds a copy of each TLP until acknowledged by thecomponent on the other side of the link, note that this may in practicebe implemented with buffering higher up the stack (in or above assembler412) and they can be stored in corresponding entries until selected fortransmission to physical layer 430 via a data/message selector 428. Ingeneral, the above-described transaction and data link layers mayoperate in accordance with conventional PCIe™ protocol stack circuitry,with certain modifications as will be described further below.

Instead with regard to physical layer 430, many more modifications ofcertain logical components of this layer, e.g., as modified from a PCIe™protocol stack may occur as well as for providing interfacing to theactual physical portions of the physical unit of another communicationprotocol. As seen, the incoming packets may be applied to a framinggenerator 432, which adds physical layer framing symbols and generatesframing for the packets and provides them to a width/location mapper 434that shifts the bytes in the datapath to generate the required alignmentfor the external transmission, adjusting datapath width if needed and inturn is coupled to a trainer and skip sequencer 436, which may be usedto perform link training and skip sequencing. As seen, framing generator432, trainer/sequencer 436 and a data/sequence selector 438 all may becoupled to a physical layer transmit controller 435 which is atransceiver portion of LTSSM and related logic. Block 436 is logic togenerate physical layer transmissions such as training sets (TS) andskip ordered sets. In this way, the framed packets may be selected andprovided to physical circuitry to perform coding, serialization anddriving of the serialized signals corresponding to the processed packetsonto a physical interconnect. In one embodiment, the mapping of symboldifferences between the different communication protocols may beperformed in the framing generator 432.

As seen, multiple individual channels or lanes can be provided for thisphysical interconnect. In the embodiment shown, each physical channel orlane can include its own independent PHY unit transmit circuitry 445₀-445 _(j), each of which in one embodiment can be part of an M-PHY unitin accordance with the MIPI specification. As described herein unlikePCIe™ where the number of transmitters and receivers match, differentnumbers of transmitters and receivers may be present. Thus as seen, eachtransmit circuit 445 can include an encoder which acts to encode symbolsaccording to an 8b/10b encoding, a serializer to serialize the encodedsymbols, and a driver to drive the signals onto the physicalinterconnect. As further seen, each lane or channel may be associatedwith a logical unit 440 ₀-440 _(j), which may be logical circuitryaccording to the MIPI specification for an M-PHY to thus manage thephysical communication via the corresponding lane.

Note that these multiple lanes can be configured to operate at differentrates, and embodiments may include different numbers of such lanes.Furthermore, it is possible to have different numbers of lanes and lanespeeds in transmit and receive directions. Thus although a given logicunit 440 controls the operation of a corresponding lane of PHY 445,understand that physical layer transmit controller 435 may act tocontrol the overall transmission of information via the physicalinterconnect. Note that in some cases, some very basic functionality isperformed by distinct logic associated with each lane; for cases wherelanes can be allocated to more than a single link, multiple LTSSMinstances may be provided; for a trained link, there is a single LTSSMin each component controlling both the transceiver and receiver sides.This overall control can include power control, link speed control, linkwidth control, initialization and so forth.

Still referring to FIG. 4, incoming information received via physicalinterconnects may similarly pass through physical layer 430, data linklayer 420, and transaction layer 410 via receive mechanism of theselayers. In the embodiment shown in FIG. 4, each PHY unit may furtherinclude receive circuitry, namely receive circuitry 455 ₀-455 _(k),which in the embodiment shown can be present for each lane of thephysical link. Note that in this embodiment, the number of receivercircuits 455 and transmitter circuits 445 is different. As seen, thisphysical circuitry can include an input buffer to receive incominginformation, a deserializer to deserialize the information, and adecoder which may act to decode the symbols communicated in an 8b/10bencoding. As further seen, each lane or channel may be associated with alogical unit 450 ₀-450 _(k), which may be logical circuitry according toa given specification (such as the MIPI specification for an M-PHY) tothus manage the physical communication via the corresponding lane.

The decoded symbols in turn may be provided to a logical portion ofphysical layer 430, which as seen may include elastic buffers 460 wherethe elastic buffer accommodates differences in clocking between thiscomponent and the other component on the link; note that its locationmay shift in various implementations, e.g., to be below the 8b/10bdecoder, or to be combined with the lane deskew buffer and to store theincoming decoded symbols. In turn, the information may be provided to awidth/location mapper 462, and from there to a lane deskew buffer 464that performs deskew across multiple lanes and for multi-lane cases,buffer 464 can handle differences in signal skew between lanes tore-align bytes. In turn, the deskewed information may be provided to aframing processor 466 which may remove framing present in the incominginformation. As seen, a physical layer receive controller 465 may becoupled to and control elastic buffers 460, mapper 462, deskew buffer464, and framing processor 466.

Still referring to FIG. 4, the recovered packets may be provided to botha receive messaging mechanism 478 and an error detector, sequencechecker and link level retry (LLR) requestor 475. This circuitry mayperform error correction checking on the incoming packets, e.g., by wayof performing CRC checksum operations, performing sequencing checks, andrequesting link level retry of packets incorrectly received. Bothreceive messaging mechanism 478 and error detector/requestor 475 may beunder control of a data link receive controller 480.

Still referring to FIG. 4, the packets thus processed in unit 475 may beprovided to transaction layer 410, and more specifically to a flowcontroller 485, which performs flow control on these packets to providethem to a packet interpreter 495. Packet interpreter 495 performsinterpretation of the packets and forwards them on to a selecteddestination, e.g., a given core or other logic circuitry of thereceiver. Although shown at this high level in the embodiment of FIG. 4,understand that the scope of the present invention is not limited inthis regard.

Note that PHYs 440 may use the same 8b/10b encoding as supported byPCIe™ for transmission. The 8b/10b encoding scheme provides specialsymbols that are distinct from data symbols used to representcharacters. These special symbols may be used for various linkmanagement mechanisms as described in the physical layer chapter of thePCIe™ specification. Additional special symbol usages by the M-PHY aredescribed in the MIPI M-PHY specification. Embodiments may provide for amapping between PCIe™ and MIPI M-PHY symbols.

Referring now to Table 1, shown is an exemplary mapping of PCIe™ symbolsto M-PHY symbols in accordance with one embodiment of the presentinvention. Thus this table shows mapping of special symbols for aconverged protocol stack in accordance with one embodiment of thepresent invention.

TABLE 1 Mapping of Control Converged MIPI M-PHY Symbols PCIe EncodingStack Mapping Comment K28.5 COM COM Marker0 K28.3 IDL IDL Marker1 K28.6Reserved SDP Marker2 Note: Map SDP here since the original PCIe encodingmaps to M-PHY reserved encoding. K23.7 PAD SKP Marker3 Note: Map SKP toneutral disparity K23.7 symbol since it does not advance thescrambler/de- scrambler. K27.7 STP STP Marker4 K29.7 END END Marker5K30.7 EDB EDB Marker6 K28.1 FTS PAD Filler Note: Map PAD here since SKPhas taken its encodings. FTS is not needed since the M-PHY SYNCmechanism can be used. M-PHY SYNC mechanism is a better option since thedefined SYNC symbols have higher edge density. RMMI spec requires M-PHYto insert Fillers when TX_DORDY is low. K28.0 SKP Reserved ReservedK28.2 SDP Reserved Reserved K28.7 EIE Reserved Reserved Note: EIE is notrequired since M-PHY squelch is detecting DIF- Z to DIF-N transition.Others Reserved Reserved Reserved

The 8b/10b decode rules are the same as defined for PCIe™ specification.The only exception for 8b/10b rules is when detecting a TAIL OF BURST,which is a specific sequence that violates the 8b/10b rules. Accordingto various embodiments, physical layer 430 can provide a notification todata link layer 420 of any errors encountered during the TAIL OF BURST.

In one embodiment, the framing and application of symbols to lanes maybe as defined in the PCIe™ specification, while data scrambling can bethe same as defined in the PCIe™ specification. Note however that thedata symbols transmitted in the PREPARE phase of a communicationaccording to the MIPI-specification are not scrambled.

With regard to link initialization and training, the link manager mayprovide for configuration and initialization of the link which asdiscussed above can include one or more channels of lanes, support ofnormal data transfers, support of state transitions when recovering fromlink errors, and port restart from a low power state.

To effect such operation, the following physical and link-relatedfeatures may be known a priori, e.g., prior to initialization: PHYparameters (e.g., including initial link speed and supported speed; andinitial link width and supported link widths).

In one embodiment, training may include various operations. Suchoperations may include initializing the link at the configured linkspeed and width, bit lock per lane, symbol lock per lane, lane polarity,and lane-to-lane deskew for multi-lane links. In this way, training candiscover lane polarity and perform adjustments accordingly. However,note that link training in accordance with an embodiment of the presentinvention may not include link data rate and width negotiation, linkspeed and width degradation. Instead as described above uponinitialization of a link, both entities a priori know the initial linkwidth and speed and thus the time and computation expense associatedwith negotiation can be avoided.

PCIe™ ordered sets can be used with the following modifications: TS1 andTS2 ordered sets are used to facilitate IP re-use but many fields of thetraining ordered sets are ignored. Also, fast training sequences are notused. An electrical idle ordered set (EIOS) may be retained tofacilitate IP re-use, as is a Skip OS, but the frequency of Skip OS maybe at a different rate than according to the PCIe™ specification. Notealso that data stream ordered sets and symbols may be the same asaccording to the PCIe™ specification.

The following events are communicated to facilitate link training andmanagement: (1) presence, which can be used to indicate that an activePHY is present on the remote end of the link; and (2) configurationready, which is triggered to indicate that PHY parameter configurationis completed and the PHY is ready operate at configured profile. In oneembodiment such information can be communicated via a consolidatedsideband signal in accordance with an embodiment of the presentinvention

For purposes of control of electrical idle situations, the PHY has aTAIL OF BURST sequence that is used to indicate that the transmitter isentering into an electrical idle state. In one embodiment, the sidebandchannel may be used to signal exit from electrical idle. Note that thisindication may be in addition to PHY squelch break mechanisms. An OPENSsequence of symbols may be transmitted as an EIOS to indicate entry intoelectrical idle state.

In some embodiments, a fast training sequence (FTS) is not defined.Instead, a PHY may use a specific physical layer sequence for exit fromstall/sleep state to a burst state that can be used to address bit lock,symbol lock and lane-to-lane de-skew. A small number of FTS can bedefined as a sequence of symbols for robustness. A start of data streamordered set may be according to the PCIe™ specification, as is linkerror recovery.

As to link data rates, in various embodiments the initial data rate atwhich the link initializes may be at a predetermined data rate. A datarate change from this initial link speed may occur by going through arecovery state. Embodiments may support asymmetric link data rates wherethe data rate is permitted to be different in opposite directions.

In one embodiment, the link widths supported may be according to thoseof the PCIe™ specification. Further, as described above, embodiments maynot support a protocol for negotiating link width as the link width ispredetermined, and as a result link training may be simplified. Ofcourse, embodiments may provide support for asymmetric link widths inopposite directions. At the same time, the initial link width and theinitial data rate to be configured for each direction of the link may bea priori known before training starts.

With respect to physical ports of the PHY unit, the ability for a xNport to form a xN link as well as a x1 link (where N can be 32, 16, 12,8, 4, 2, and 1) is not required and the ability for a xN port to formany link width between N and 1 is optional. An example of this behaviorincludes a x16 port, which can only configure into only one link, butthe width of the link can be configured to be x12, x8, x4, x2 as well asrequired widths of x16 and x1. As such, designers seeking to implementdevices using a protocol stack in accordance with an embodiment of thepresent invention can connect ports between two different components ina way that allows those components to meet the above requirements. Ifthe ports between components are connected in ways that are notconsistent with intended usage as defined by the component's portdescriptions/data sheets, behavior is undefined.

In addition, the ability to split a port into two or more links is notprohibited. If such support is appropriate for a given design, the portcan be configured to support a specific width during training. Anexample of this behavior would be a x16 port that may be able toconfigure two x8 links, four x4 links, or 16 x1 links.

When using 8b/10b encoding, an unambiguous lane-to-lane de-skewmechanism, as in the PCIe™ specification, is the COM symbol of orderedsets received during training sequence or SKP ordered sets, sinceordered sets are transmitted simultaneously on all lanes of a configuredlink. The MK0 symbol transmitted during the sync sequence of HS-BURSTmay be used for lane-lane de-skew.

As briefly described above with regard to FIG. 4, a link training andstate manager can be configured to perform various operations, includingadapting the upper layers of a PCIe™ protocol stack to a lower layer PHYunit of a different protocol. Furthermore, this link manager canconfigure and manage single or multiple lanes and may include supportfor a symmetric link bandwidth, compatibility of the state machine withPCIe™ transaction and data link layers, link training, optionalsymmetric link stall states, and control of sideband signals for robustcommunications. Accordingly, embodiments provide for implementing PCIe™transaction and data link layers with limited modifications to accountfor different link speeds and asymmetric links. Furthermore, using alink manager in accordance with an embodiment of the present invention,support for multi-lane, asymmetric link configuration, sidebandconsolidation and dynamic bandwidth scalability can be realized, whilefurther enabling bridging between layers of different communicationprotocols.

Referring now to FIG. 5, shown is a state diagram 500 for a linktraining state machine, which can be part of a link manager inaccordance with an embodiment of the present invention. As shown in FIG.5, link training can begin in a detection state 510. This state occurson power on reset and is applicable both to upstream and downstreamports. After reset completion, all configured lanes may transition to agiven state, namely a HIBERN8 state, upon which each end of the link cansignal, e.g., via a PRESENCE signal using a sideband channel. Note thatin this detection state, a high impedance signal, namely a DIF-Z signal,may be driven on all lanes.

Thus control passes from detect state 510 to configuration state 520when the PRESENCE event is signaled and received, and this highimpedance is driven on all configured lanes. In configuration state 520,the PHY parameters can be configured and upon completion on allconfigured lanes of each end of the link, a configuration ready signal(CFG-RDY) can be indicated, e.g., using the sideband interconnect, whilethe high impedance is maintained on all lanes.

Thus upon the sending and receiving of this configuration readyindication via the sideband interconnect, control passes to a stallstate 530. Namely in this L0.STALL state, the PHY transitions to a STALLstate and continues to drive the high impedance on all configured lanes.As seen, depending on whether data is available for transmission orreceipt control can pass to an active state L1 (state 530), a low powerstate (L1 state 540), a deeper low power state (L1.OFF state 545), orback to configuration state 520.

Thus in the STALL state, a negative drive signal DIF-N can becommunicated on all configured lanes. Then when directed by theinitiator a BURST sequence may begin. Accordingly, control passes toactive state 530 after transmission of a MARKER 0 (MK0) symbol.

In one embodiment, a receiver may detect exit from the STALL state onall configured lanes and perform a bit lock and symbol lock according,e.g., to the MIPI specification. In embodiments with a multi-lane link,this MK0 symbol may be used to establish lane-to-lane deskew.

Instead when directed to a low power state (namely the L1 state 540),all configured lanes may transition to a SLEEP state. In turn whendirected to a deeper low power state (namely L1.OFF state 545), allconfigured lanes may transition to the HIBERN8 state. Finally, whendirected back to the configuration state, similarly all configured lanestransition to the HIBERN8 state.

Still referring to FIG. 5, for active data transfer, control thus passesto active state 550. Specifically, this is the state where link andtransaction layers begin exchanging information using data link layerpackets (DLLPs) and TLPs. As such, a payload transfer can occur and atthe conclusion of such transfer, a TAIL of BURST symbol can becommunicated.

As seen, from this active state control can pass back to STALL state530, to a recovery state 560, e.g., responsive to a receiver error orwhen otherwise directed, or to a deeper low power (e.g., an L2) state570.

To return to the stall state, the transmitter may send an EIOS sequencefollowed by a TAIL of BURST indication on all configured lanes.

If an error occurs or otherwise as directed, control can also pass torecovery state 560. Here, a transition to recovery causes all configuredlanes in both directions to enter into the STALL state. To effect this,a GO TO STALL signal can be sent on the sideband interconnect and thetransmitter of this signal can wait for a response. When this stallsignal has been sent and received, as indicated by a received GO TOSTALL indication on the sideband interconnect, control passes back toSTALL state 530. Note that this recovery state thus establishes theprotocol using the sideband to coordinate simultaneous entry into theSTALL state.

With regard to low power states L1 and L1.OFF, operation is according tostates 540 and 545. Specifically, control passes to the L1 lower powerstate 540 from the STALL state so that the PHY can be placed into aSLEEP state. In this state, a negative drive signal, namely a DIF-Nsignal can be driven on all configured lanes. When directed to exit thestate, control passes back to STALL state 530, e.g., via signaling of aPRESENCE signal over the sideband interconnect.

As also seen, the deeper low state L1.OFF can be entered when all L1.OFFconditions have been met. In one embodiment, these conditions mayinclude completely power gating or turning off power to the PHY unit. Inthis deeper low power state, the PHY may be placed in the HIBERN8 state,and the high impedance signal driven on all configured lanes. To exitthis state, control passes back to the STALL state, via driving of DIF-Non all configured lanes.

As further seen in FIG. 5, additional states can be present, namely astill further deeper low power state (L2) 570, which can be entered froman active state when power is ready to turn off. In one embodiment, thisstate may be the same as that of the PCIe™ specification.

Referring now to Table 2, shown is a mapping between LTSSM statesaccording to the PCIe™ specification and corresponding M-PHY states inaccordance with an embodiment of the present invention.

TABLE 2 LTSSM State M-PHY State Details Detect, Polling SAVE Statetransitions through SAVE sub-states Configuration BURST BURST (PREP,SYNC) sub-states Recovery BURST/SLEEP/ May be in BURST state but willSTALL transition to BURST through SLEEP/STALL L0 BURST (payload) BURSTmode and exchange transactions L0s STALL STALL state L1 SLEEP SLEEPstate L1.OFF HIBERN8 HIBERN8 L2 UNPOWERED UNPOWERED state DisabledDISABLED DISABLED state Loopback No action Link speed may change onentry to Loopback from Configuration Hot Reset INLINE RESET IN-LINERESET state

As described above with regard to FIG. 2, embodiments provide for aconsolidated sideband mechanism that can be used for link management,along with optional in-band support. In this way, using the sidebandcircuitry and interconnect, link management and control can occurindependently of the higher speed (and greater power consuming)circuitry of the physical layer for the primary interconnect. Further inthis way, this sideband channel can be used when the portions of the PHYunit associated with the primary interconnect are powered off, enablingreduced power consumption. Also, this consolidated sideband mechanismcan be used before training of the primary interconnect, and also may beused when a failure is present on the primary interconnect.

Still further, via this consolidated sideband mechanism, a singleinterconnect, e.g., a pair of differential wires in each direction canbe present, reducing both pin counts and enabling the addition of newcapabilities. Embodiments may also enable faster and more robustclock/power gating and can remove ambiguities in conventional protocolssuch as PCIe™ sideband mechanism using this link.

Although the scope of the present invention is not limited in thisregard, in different embodiments the sideband interconnect (e.g.,sideband interconnect 270 of FIG. 2) can be implemented as a single wirebidirectional sideband signal, a dual-wire dual-direction unidirectionalset of signals, a low speed in-band signaling mechanism such asavailable using an M-PHY in a low power pulse width modulation (PWM)mode or as an in-band high speed signaling mechanism such as physicallayer ordered sets or DLLPs.

As examples and not for purposes of limitation, various physical layerapproaches may be supported. A first approach can be a single-wirebidirectional sideband signal providing lowest pin count when a sidebandinterconnect is used. In some embodiments, this signal can bemultiplexed on an existing sideband, e.g., PERST#, WAKE# or CLKREQsignals. A second approach may be a dual-wire dual-directionunidirectional set of signals, which may be simpler and somewhat moreefficient compared to the single-wire approach, but at the cost of anadditional pin. Such implementation can be multiplexed on existingsidebands, e.g., PERST# for host device and CLKREQ# for device host (inthis example, the existing signal directionality is maintained,simplifying bi-modal implementations). A third approach may be alow-speed in-band signaling mechanism, such as M-PHY LS PWM modes, whichreduces pin count relative to sideband mechanisms, and may still supportsimilarly low power levels. Because this mode of operation is mutuallyexclusive with high-speed operation, it could be combined with ahigh-speed in-band mechanism such as physical layer ordered sets orDLLP. While this approach is not low power, it maximizes commonalitywith existing high-speed IO. When combined with low speed in-bandsignaling, this approach may provide a good low power solution.

To realize one or more of these configurations in a given system, asemantic layer can be provided, which can be used to determine themeaning of the information to be exchanged over the physical layer, aswell as a policy layer, which can be used to comprehend thedevice/platform level action/reactions. In one embodiment these layersmay be present in a SB PHY unit.

By providing a layered approach, embodiments allow for differentphysical layer implementations that may include both sidebandcapabilities (which may be preferred in some implementations due tosimplicity and/or low power operation) and in-band, which may bepreferred for other implementations, e.g., avoiding the need foradditional pin count.

In one embodiment, a number of sideband signals can be configured, e.g.,via the semantic layer into a single packet for communication via theconsolidated sideband mechanism (or an in-band mechanism). In oneembodiment, Table 3 below shows the various signals that may be presentin one embodiment. In the Table shown, the logical direction of thesignals is shown by the arrow, where an up arrow is defined to be thedirection to the host (e.g., a root complex) and the down arrow isdefined to be the direction to the device (e.g., a peripheral devicesuch as a radio solution).

TABLE 3 Device Present ↑ Power Good ↓ Power Off ↓ Refclock Good ↓Fundamental Reset ↓ Config Ready ↑↓ Ready to Train ↑↓ Start Training ↑↓L1pg Request↑↓ L1pg Reject ↑↓ L1pg Grant↑↓ OBFF CPU Active ↓ OBFF DMA ↓OBFF Idle ↓ Wakeup ↑ Ack receipt of handshake ↑↓

Referring now to FIG. 6, shown is a flow diagram for the various statesof a sideband mechanism in accordance with an embodiment of the presentinvention. As shown in FIG. 6, these various states may be with regardto the root complex (e.g., host-controlled operation). State diagram 600may provide for control of the various states via the host. As seen,operation begins in a pre-boot state 610 in which a presence signal canbe communicated. Note that this presence signal may be as describedabove with regard to link management operations. Then control passes toa boot state 620 in which various signals may be communicated, namely apower good signal, a reset signal, a reference clock state signal and aready to train signal. Note that all of these signals can becommunicated via a single packet in which each of these signals cancorrespond to an indicator or field of the packet (e.g., a one bitindicator of the packet).

Still referring to FIG. 6, control passes next to an active state 630 inwhich a system may be in an active state (e.g., S0), a correspondingdevice (e.g., the downstream device may be an active device state (e.g.,D0) and link may be in an active state, stall, or low power state (e.g.,L0, L0 s, or L1). As seen, in this state various signals can becommunicated, including an OBFF signal, a clock request signal, areference clock state, a request L0 signal and a ready to train signal.

Next, control can pass to a low power state 640, e.g., after the abovesignaling has been performed. As seen, in this low power state 640, thesystem may be in an active state while the device may be in a relativelylow latency low power state (e.g., D3 hot). In addition, the link may bein a given low power state (e.g., L2 or L3). As seen in these states,the signals communicated via the consolidated sideband packet mayinclude a wakeup signal, a reset signal, and a power good signal.

As the system goes into deeper low power states, a second low powerstate 650 can be entered (e.g., when the system is in an S0 state andthe device is in a D3 cold state, and the link is similarly in an L2 orL3 state. As seen, the same wakeup, reset and power good signals can becommunicated. Also seen in FIG. 6, the same signals can occur in adeeper power state 660 (e.g., a system low power state, S3) and a devicelow power state (e.g., D3 cold), and the same link low power states L2and L3. Although shown with this particular set of sideband informationcommunicated, understand the scope of the present invention is notlimited in this regard.

Embodiments thus provide a layered structure with extensibility that canbalance simplicity and low latency versus flexibility. In this way,existing sideband signals and additional sideband signals can bereplaced with a smaller number of signals, and enable future expansionof sideband mechanisms without addition of more pins.

Referring now to FIG. 7, shown is a flow diagram of a method inaccordance with an embodiment of the present invention. As shown in FIG.7, method 700 may be used to communicate data via a converged protocolstack that includes upper layers of one communication protocol and alower, e.g., physical layer of a different communication protocol. Inthe examples shown assume a converged protocol stack as described above,namely with upper transaction and data link layers of a PCIe™ protocoland a physical layer of a different specification, e.g., a MIPIspecification. Of course, additional logic to enable the convergence ofthese two communication protocols into a single protocol stack also maybe present, such as the logic and circuitry discussed above with regardto FIG. 4.

As seen in FIG. 7, method 700 can begin by receiving a first transactionin a protocol stack of the first communication protocol (block 710). Forexample, various logic of a root complex such as a core, other executionengine or so forth seeks to send information to another device.Accordingly, this information may pass to the transaction layer. Asseen, control passes to block 720 where the transaction can be processedand provided to a logical portion of a PHY of a second communicationprotocol. This processing may include the various operations discussedabove with regard to the flow through FIG. 4 where different operationsto receive data, perform flow control, link operations, packetizingoperations and so forth can occur. In addition, various operations toprovide a data link layer packet to a PHY can occur. Next, controlpasses to block 730 where this first transaction can be converted in alogical portion of the PHY to a second format transaction. For exampleany conversion of the symbols (if needed) can be performed. In addition,the various translation operations done to thus render the transactioninto a format for transmission on the link can occur. Accordingly,control can pass to block 740 where this second formatted transactioncan be communicated from the PHY to the device via a link. As anexample, the second format transaction can be the serialized data afterline coding, serialization and so forth. Although shown at this highlevel in the embodiment of FIG. 7, understand the scope of the presentinvention is not limited in this regard.

Referring now to FIG. 8, shown is a block diagram of components presentin a computer system in accordance with an embodiment of the presentinvention. As shown in FIG. 8, system 800 can include many differentcomponents. These components can be implemented as ICs, portionsthereof, discrete electronic devices, or other modules adapted to acircuit board such as a motherboard or add-in card of the computersystem, or as components otherwise incorporated within a chassis of thecomputer system. Note also that the block diagram of FIG. 8 is intendedto show a high level view of many components of the computer system.However, it is to be understood that additional components may bepresent in certain implementations and furthermore, differentarrangement of the components shown may occur in other implementations.

As seen in FIG. 8, a processor 810, which may be a low power multicoreprocessor socket such as an ultra low voltage processor, may act as amain processing unit and central hub for communication with the variouscomponents of the system. Such processor can be implemented as a SoC. Inone embodiment, processor 810 may be an Intel® Architecture Core™-basedprocessor such as an i3, i5, i7 or another such processor available fromIntel Corporation, Santa Clara, Calif. However, understand that otherlow power processors such as available from Advanced Micro Devices, Inc.(AMD) of Sunnyvale, Calif., an ARM-based design from ARM Holdings, Ltd.or a MIPS-based design from MIPS Technologies, Inc. of Sunnyvale,Calif., or their licensees or adopters may instead be present in otherembodiments such as an Apple A5 processor.

Processor 810 may communicate with a system memory 815, which in anembodiment can be implemented via multiple memory devices to provide fora given amount of system memory. As examples, the memory can be inaccordance with a Joint Electron Devices Engineering Council (JEDEC) lowpower double data rate (LPDDR)-based design such as the current LPDDR2standard according to JEDEC JESD 209-2E (published April 2009), or anext generation LPDDR standard to be referred to as LPDDR3 that willoffer extensions to LPDDR2 to increase bandwidth. As examples, 2/4/8gigabytes (GB) of system memory may be present and can be coupled toprocessor 810 via one or more memory interconnects. In variousimplementations the individual memory devices can be of differentpackage types such as single die package (SDP), dual die package (DDP)or quad die package (QDP). These devices can in some embodiments bedirectly soldered onto a motherboard to provide a lower profilesolution, while in other embodiments the devices can be configured asone or more memory modules that in turn can couple to the motherboard bya given connector.

To provide for persistent storage of information such as data,applications, one or more operating systems and so forth, a mass storage820 may also couple to processor 810. In various embodiments, to enablea thinner and lighter system design as well as to improve systemresponsiveness, this mass storage may be implemented via a SSD. Howeverin other embodiments, the mass storage may primarily be implementedusing a hard disk drive (HDD) with a smaller amount of SSD storage toact as a SSD cache to enable non-volatile storage of context state andother such information during power down events so that a fast power upcan occur on re-initiation of system activities. Also shown in FIG. 8, aflash device 822 may be coupled to processor 810, e.g., via a serialperipheral interface (SPI). This flash device may provide fornon-volatile storage of system software, including a basic input/outputsoftware (BIOS) as well as other firmware of the system.

Various input/output (IO) devices may be present within system 800.Specifically shown in the embodiment of FIG. 8 is a display 824 whichmay be a high definition LCD or LED panel configured within a lidportion of the chassis. This display panel may also provide for a touchscreen 825, e.g., adapted externally over the display panel such thatvia a user's interaction with this touch screen, user inputs can beprovided to the system to enable desired operations, e.g., with regardto the display of information, accessing of information and so forth. Inone embodiment, display 824 may be coupled to processor 810 via adisplay interconnect that can be implemented as a high performancegraphics interconnect. Touch screen 825 may be coupled to processor 810via another interconnect, which in an embodiment can be an I²Cinterconnect. As further shown in FIG. 8, in addition to touch screen825, user input by way of touch can also occur via a touch pad 830 whichmay be configured within the chassis and may also be coupled to the sameI²C interconnect as touch screen 825.

For perceptual computing and other purposes, various sensors may bepresent within the system and can be coupled to processor 810 indifferent manners. Certain inertial and environmental sensors may coupleto processor 810 through a sensor hub 840, e.g., via an I²Cinterconnect. In the embodiment shown in FIG. 8, these sensors mayinclude an accelerometer 841, an ambient light sensor (ALS) 842, acompass 843 and a gyroscope 844. Other environmental sensors may includeone or more thermal sensors 846 which may couple to processor 810 via asystem management bus (SMBus) bus, in one embodiment. Understand alsothat one or more of the sensors can couple to processor 810 via a LPSlink in accordance with an embodiment of the present invention.

Also seen in FIG. 8, various peripheral devices may couple to processor810 via a low pin count (LPC) interconnect. In the embodiment shown,various components can be coupled through an embedded controller 835.Such components can include a keyboard 836 (e.g., coupled via a PS2interface), a fan 837, and a thermal sensor 839. In some embodiments,touch pad 830 may also couple to EC 835 via a PS2 interface. Inaddition, a security processor such as a trusted platform module (TPM)838 such as in accordance with the Trusted Computing Group (TCG) TPMSpecification Version 1.2 (Oct. 2, 2003), may also couple to processor810 via this LPC interconnect.

System 800 can communicate with external devices in a variety ofmanners, including wirelessly. In the embodiment shown in FIG. 8,various wireless modules, each of which can correspond to a radioconfigured for a particular wireless communication protocol, arepresent. One manner for wireless communication in a short range such asa near field may be via a near field communication (NFC) unit 845 whichmay communicate, in one embodiment with processor 810 via an SMBus. Notethat via this NFC unit 845, devices in close proximity to each other cancommunicate. For example, a user can enable system 800 to communicatewith another (e.g.,) portable device such as a smartphone of the uservia adapting the two devices together in close relation and enablingtransfer of information such as identification information paymentinformation, data such as image data or so forth. Wireless powertransfer may also be performed using a NFC system.

As further seen in FIG. 8, additional wireless units can include othershort range wireless engines including a WLAN unit 850 and a Bluetoothunit 852. Using WLAN unit 850, Wi-Fi™ communications in accordance witha given Institute of Electrical and Electronics Engineers (IEEE) 802.11standard can be realized, while via Bluetooth unit 852, short rangecommunications via a Bluetooth protocol can occur. These units maycommunicate with processor 810 via, e.g., a USB link or a universalasynchronous receiver transmitter (UART) link. Or these units may coupleto processor 810 via an interconnect via a low power interconnect suchas a converged PCIe/MIPI interconnect as described herein, or anothersuch protocol such as a serial data input/output (SDIO) standard. Ofcourse, the actual physical connection between these peripheral devices,which may be configured on one or more add-in cards, can be by way ofthe NGFF connectors adapted to a motherboard.

In addition, wireless wide area communications, e.g., according to acellular or other wireless wide area protocol, can occur via a WWAN unit856 which in turn may couple to a subscriber identity module (SIM) 857.In addition, to enable receipt and use of location information, a GPSmodule 855 may also be present. Note that in the embodiment shown inFIG. 8, WWAN unit 856 and an integrated capture device such as a cameramodule 854 may communicate via a given USB protocol such as a USB 2.0 or3.0 link, or a UART or I²C protocol. Again the actual physicalconnection of these units can be via adaptation of a NGFF add-in card toan NGFF connector configured on the motherboard.

To provide for audio inputs and outputs, an audio processor can beimplemented via a digital signal processor (DSP) 860, which may coupleto processor 810 via a high definition audio (HDA) link. Similarly, DSP860 may communicate with an integrated coder/decoder (CODEC) andamplifier 862 that in turn may couple to output speakers 863 which maybe implemented within the chassis. Similarly, amplifier and CODEC 862can be coupled to receive audio inputs from a microphone 865 which in anembodiment can be implemented via dual array microphones to provide forhigh quality audio inputs to enable voice-activated control of variousoperations within the system. Note also that audio outputs can beprovided from amplifier/CODEC 862 to a headphone jack 864.

Embodiments thus can be used in many different environments. Referringnow to FIG. 9, shown is a block diagram of an example system 900 withwhich embodiments can be used. As seen, system 900 may be a smartphoneor other wireless communicator. As shown in the block diagram of FIG. 9,system 900 may include a baseband processor 910 which may be a multicoreprocessor that can handle both baseband processing tasks as well asapplication processing. Thus baseband processor 910 can perform varioussignal processing with regard to communications, as well as performcomputing operations for the device. In turn, baseband processor 910 cancouple to a user interface/display 920 which can be realized, in someembodiments by a touch screen display. In addition, baseband processor910 may couple to a memory system including, in the embodiment of FIG. 9a non-volatile memory, namely a flash memory 930 and a system memory,namely a dynamic random access memory (DRAM) 935. As further seen,baseband processor 910 can further couple to a capture device 940 suchas an image capture device that can record video and/or still images.

To enable communications to be transmitted and received, variouscircuitry may be coupled between baseband processor 910 and an antenna980. Specifically, a radio frequency (RF) transceiver 970 and a wirelesslocal area network (WLAN) transceiver 975 may be present. In general, RFtransceiver 970 may be used to receive and transmit wireless data andcalls according to a given wireless communication protocol such as 3G or4G wireless communication protocol such as in accordance with a codedivision multiple access (CDMA), global system for mobile communication(GSM), long term evolution (LTE) or other protocol. Other wirelesscommunications such as receipt or transmission of radio signals, e.g.,AM/FM, or global positioning satellite (GPS) signals may also beprovided. In addition, via WLAN transceiver 975, local wireless signals,such as according to a Bluetooth™ standard or an IEEE 802.11 standardsuch as IEEE 802.11a/b/g/n can also be realized. Note that the linkbetween baseband processor 910 and one or both of transceivers 970 and975 may be via a low power converged interconnect that combines and mapsfunctionality of a PCIe™ interconnect and a low power interconnect suchas a MIPI interconnect. Although shown at this high level in theembodiment of FIG. 9, understand the scope of the present invention isnot limited in this regard.

Embodiments may be used in many different types of systems. For example,in one embodiment a communication device can be arranged to perform thevarious methods and techniques described herein. Of course, the scope ofthe present invention is not limited to a communication device, andinstead other embodiments can be directed to other types of apparatusfor processing instructions, or one or more machine readable mediaincluding instructions that in response to being executed on a computingdevice, cause the device to carry out one or more of the methods andtechniques described herein.

Embodiments may be implemented in code and may be stored on anon-transitory storage medium having stored thereon instructions whichcan be used to program a system to perform the instructions. The storagemedium may include, but is not limited to, any type of disk includingfloppy disks, optical disks, solid state drives (SSDs), compact diskread-only memories (CD-ROMs), compact disk rewritables (CD-RWs), andmagneto-optical disks, semiconductor devices such as read-only memories(ROMs), random access memories (RAMs) such as dynamic random accessmemories (DRAMs), static random access memories (SRAMs), erasableprogrammable read-only memories (EPROMs), flash memories, electricallyerasable programmable read-only memories (EEPROMs), magnetic or opticalcards, or any other type of media suitable for storing electronicinstructions.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

The invention claimed is:
 1. A system on a chip (SoC) comprising: aprotocol stack for a Peripheral Component Interconnect Express™ (PCIe™)load/store input/output communication protocol, the protocol stack beinga transaction layer and a link layer; a physical (PHY) unit coupled tothe protocol stack to provide communication between the SoC and a devicecoupled to the SoC via a physical link, the PHY unit of a low powercommunication protocol and including a physical unit circuit accordingto the low power communication protocol and a logical layer to interfacethe protocol stack to the physical unit circuit, the logical layerincluding a link training state machine to perform link training of thephysical link and including a mapping logic to map first special symbolsof the PCIe™ load/store input/output communication protocol to secondspecial symbols of the low power communication protocol; and a secondPHY unit separate from the PHY unit to provide communication between theSoC and the device via a sideband channel separate from the physicallink, the sideband channel comprising a serial link, wherein the secondPHY unit is to transmit a first presence signal to the device and toreceive a second presence signal from the device, the link trainingstate machine to configure the physical link responsive to receipt ofthe second presence signal in the second PHY unit.
 2. The SoC of claim1, wherein the physical link has an asymmetric width from the SoC to thedevice as from the device to the SoC, and the physical link isconfigurable to operate at an asymmetric frequency from the SoC to thedevice as from the device to the SoC.
 3. The SoC of claim 1, wherein thelink training state machine is to a priori initialize the physical linkto an initial link width and frequency from a reset of the SoC without anegotiation with the device.
 4. The SoC of claim 3, wherein the linktraining state machine is to cause a change in a link width of thephysical link without a negotiation with the device.
 5. A methodcomprising: performing, in a first integrated circuit coupled to asecond integrated circuit via a physical link, a detection state of alink training state machine of a physical (PHY) unit of a low powercommunication protocol including a physical unit circuit, the PHY unitcoupled to a protocol stack for a Peripheral Component InterconnectExpress™ (PCIe™) load/store input/output communication protocol being atransaction layer and a link layer, responsive to power on of the firstintegrated circuit; performing, in the first integrated circuit, aconfiguration state of the link training state machine after performingthe detection state, including sending a configuration ready signal tothe second integrated circuit via a sideband link coupled between thefirst and second integrated circuits; and performing, in the firstintegrated circuit, a stall state of the link training state machineresponsive to receipt of a second configuration ready signal from thesecond integrated circuit via the sideband link, wherein the PHY unit isto drive a differential-N signal on the physical link during the stallstate, wherein the first integrated circuit is further coupled to thesecond integrated circuit via the sideband link comprising a seriallink, the first integrated circuit having a second PHY unit separatefrom the PHY unit to transmit a first presence signal to the secondintegrated circuit and to receive a second presence signal from thesecond integrated circuit, the link training state machine to configurethe physical link responsive to receipt of the second presence signal inthe second PHY unit.
 6. The method of claim 5, further comprisinginitiating a burst sequence in the stall state to transition into anactive state of the link training state machine.
 7. The method of claim6, further comprising communicating a payload from the first integratedcircuit to the second integrated circuit in the active state andthereafter communicating a tail of burst signal to transition to thestall state.
 8. The method of claim 6, further comprising transitioningfrom the active state to a recovery state responsive to a receivererror.
 9. The method of claim 6, further comprising transitioning fromthe active state to a power off state responsive to a communicationreceived in the PHY unit from the protocol stack.
 10. The method ofclaim 5, further comprising transitioning from the stall state into afirst low power state and driving the differential-N signal on thephysical link in the first low power state.
 11. The method of claim 10,further comprising transitioning from the first low power state to thestall state responsive to receipt of a presence signal from the secondintegrated circuit via the sideband link.
 12. The method of claim 10,further comprising transitioning to a second low power state from thestall state when a set of predetermined conditions have been met, thesecond low power state lower than the first low power state, and drivinga differential high impedance signal on the physical link in the secondlow power state.
 13. The method of claim 5, further comprising: sendinga stall initiation signal to the second integrated circuit via thesideband channel; and transitioning to the stall state responsive toreceipt of a stall indication signal from the second integrated circuitvia the sideband link.
 14. A system comprising: a multicore processorincluding a plurality of cores and a protocol stack to enablecommunication between the multicore processor and a peripheral devicevia a physical link, the protocol stack including: a transaction layerin accordance with a Peripheral Component Interconnect Express (PCIe™)load/store input/output communication protocol; a data link layer inaccordance with the PCIe™ load/store input/output communicationprotocol; and a physical layer including a physical layer transmitcontroller and a physical (PHY) unit transmit circuit according to a lowpower communication protocol, wherein the physical layer transmitcontroller is to adapt the PHY unit transmit circuit to the transactionlayer and the data link layer of the PCIe™ communication protocol, thephysical layer further including a link training state machine toperform link training of the physical link and including a mapping logicto map first special symbols of the PCIe™ load/store input/outputcommunication protocol to second special symbols of the low powercommunication protocol; and the peripheral device coupled to themulticore processor via the physical link and a sideband link comprisinga serial link, wherein the multicore processor further includes a secondPHY unit separate from the PHY unit to transmit a first presence signalto the peripheral device and to receive a second presence signal fromthe peripheral device, the link training state machine to configure thephysical link responsive to receipt of the second presence signal in thesecond PHY unit.
 15. The system of claim 14, wherein the link trainingstate machine is to, responsive to power on of the multicore processor,perform a configuration state of the link training state machine afterperforming a detection state, including sending a configuration readysignal to the peripheral device via a sideband link coupled between themulticore processor and the peripheral device, and perform a stall stateof the link training state machine responsive to receipt of a secondconfiguration ready signal from the peripheral device via the sidebandlink, wherein the PHY unit transmit circuit is to drive a differential-Nsignal on the physical link during the stall state.
 16. The system ofclaim 15, wherein the link training state machine is to initiate a burstsequence in the stall state to transition into an active state of thelink training state machine, and communicate a payload from themulticore processor to the peripheral device in the active state andthereafter communicate a tail of burst signal to transition to the stallstate.
 17. The system of claim 16, wherein the link training statemachine is to signal a stall initiation signal to the peripheral devicevia the sideband link, and transition to the stall state responsive toreceipt of a stall indication signal from the peripheral device via thesideband link.
 18. The system of claim 14, wherein the peripheral devicecomprises a multi-radio integrated circuit.